The present invention generally relates to a silicon etching apparatus and, more particularly, to a silicon etching apparatus using XeF2.
There are a variety of etching reagents used for silicon bulk etching to accurate dimensions, ranging from a liquid type etchant such as ethylene diamine pyrocatechol (EDP) and KOH to high energy plasma Type etchants based on Cl2 or SF6 gases. These etching reagents may provide much flexibility and controllability in the manufacture of accurately defined microstructures but have a limitation on use due to the limited selectivity with respect to general materials such as photoresist or oxide commonly used as a masking layer in the etching process.
Xenon difluoride (hereinafter, referred to as xe2x80x9cXeF2xe2x80x9d) is a silicon etching reagent in a dry gas phase which presents several advantages over the above silicon etching reagents. XeF2 is a white solid at the room temperature under the atmospheric pressure and sublimates at the room temperature (25xc2x0 C.) under a pressure less than 3.8 Torr. An etching method using sublimated XeF2 has a high selectivity to photoresist, oxide or aluminum layers and enables etching silicon in the gas phase, thus preventing the resulting structure adhering to the substrate. Also, such an etching method enables rapid etching of the bottom surface of a large-sized silicon structure due to an isotropic etching characteristic and a high etching rate of several xcexcm/min. This etching method using XeF2 alone neither forms a polymer layer nor leaves other contaminants on the etched surfaces.
A conventional silicon etching apparatus using XeF2 is composed of a loading chamber for loading XeF2, an expansion chamber for collecting sublimated XeF2 gas, and an etching chamber for performing an etching process.
Several conventional XeF2-based silicon etching apparatuses of the above structure involve some problems as follows:
First, during the silicon etching process using XeF2, air moisture existing in the etching apparatus associates fluorine with hydrogen to form hydrofluoric acid(HF), which may damage a silicon oxide layer used as a profile protecting layer of the silicon. It is thus required to dehumidify the inside of the apparatus completely prior to the XeF2-based silicon etching process.
Second, the XeF2-based etching may not be performed uniformly even on a full silicon wafer, because the etching occurs further in a portion having a denser XeF2 gas on the surface of the silicon wafer than a portion with less dense XeF2 gas. So, the etching uniformity depends on how the XeF2 gas is uniformly distributed all over the surface of the target wafer.
Third, sublimation of the residual XeF2 in the loading chamber may be problematic. It is general that the remaining XeF2 after the etching process is reserved in the loading chamber for future uses, with the loading chamber maintained under vacuum according to the vacuum-based maintenance and control method. However, XeF2 continuously sublimates in the loading chamber at the room temperature under a pressure less than 3.8 Torr. Such a sublimation of XeF2 causes unnecessary consumption of an expensive material and association of the sublimated XeF2 gas with air moisture to corrode the chamber and other connected, annexed parts.
Finally, it is hard to measure the amount of the residual XeF2 in the loading chamber. The conventional XeF2-based silicon etching apparatus has a window on the loading chamber for visual checking the amount of the residual XeF2 in the chamber after the completion of the etching process. Such a visual check is a troublesome method and sometimes impossible when HF is formed from the sublimated XeF2 associating with air moisture to corrode the window of the loading chamber cloudy.
The present invention is to solve the problems with the conventional XeF2-based silicon etching apparatus and it is therefore an object of the present invention to provide a XeF2-based silicon etching apparatus capable of eliminating the internal air moisture to minimize damages on a silicon oxide layer.
It is another object of the present invention to provide a XeF2 -based silicon etching apparatus enabling uniform etching of a full silicon wafer.
If is further another object of the present invention to provide a XeF2-based silicon etching apparatus capable of preventing sublimation of the residual XeF2 in a loading chamber.
It is still another object of the present invention to provide a XeF2-based silicon etching apparatus capable of measuring the amount of the residual XeF2 in the loading chamber.
To achieve the above objects, there is provided a silicon etching apparatus using XeF2 including: a basic structure composed of a loading chamber for loading XeF2, an expansion chamber for collecting sublimated XeF2 gas, and an etching chamber for performing an etching process; and a means for injecting nitrogen prior to the etching process to eliminate air moisture in the apparatus and thus preventing the formation of HF.
The silicon etching apparatus using XeF2 further includes an injector having a predefined shape provided in the etching chamber for uniformly injecting the XeF2 gas on the surface of a wafer.
The silicon etching apparatus using XeF2 further includes a feedback controller for feedback controlling the internal pressure of the loading chamber in order to prevent sublimation of the residual XeF2 in the loading chamber.
The silicon etching apparatus using XeF2 further includes a weight scale for measuring the weight of remaining XeF2 in the loading chamber.